The invention relates generally to mechanical seals, and, more particularly, to a mechanical seal having a wavy face seal ring for operation in liquid and gas environments.
It has long been popular in industry to use mechanical seals to resist leaks within a variety of machines having rotating parts, including pumps, compressors and the like. More recently, mechanical seals with wavy-shaped faces have been used in these machines to minimize leakage while providing both static and dynamic load support. Examples of wavy face seal rings are described in U.S. Pat. Nos. 4,836,561 and 4,887,395 to Lebeck et al., both of which are incorporated herein by reference.
FIG. 1 illustrates a cross sectional assembly view of a pump incorporating a conventional wavy face mechanical seal. Briefly, the pump includes a housing 10, a rotating shaft 12, a wavy face seal mating ring 14, a flat-faced primary ring 16, springs 18 and a secondary seal 20, such as an O-ring. The rotating shaft extends through the primary ring and the mating ring. The primary ring rotates with the shaft while the mating ring is fixed relative to the housing. The springs urge the primary ring toward the mating ring to form the seal. In particular, the mating ring 14 and the primary ring 16 serve the primary function of sealing a sliding interface 15 between the two rings 14 and 16 by maintaining either a close gap or contact between the faces of the two rings 14 and 16 so as to limit the amount of leakage flow.
The wavy face mating ring 14 is shown in exaggerated detail in FIG. 2. The wavy face of the ring includes numerous circumferential waves 22. Each pair of waves is separated by a radially-tilted region 24. The face of the mating ring further includes an elevated and generally flat circumferential dam 26 located on its inner periphery. The waves have low spots 28 and high spots 30 that are most apparent at the outer diameter of the mating ring. Each low spot coincides with an associated low spot of a tilted region. The high spots of the waves are generally aligned in height with the dam and thus the amplitude of the waves diminishes to zero as one moves radially inward toward the dam. The waves and tilted regions tend to enhance lubrication between the mating ring and the primary ring, while the dam abuts the surface of the primary ring to minimize leakage.
The surface finish of the wavy face seal ring is particularly important in gas seal applications. In particular, a wavy face seal ring with a very smooth surface provides less leakage and greater load support. The shape of the wavy face seal ring described above is formed by grinding hard ring material 32 with a grinding machine 34 having a grinding wheel 36, as illustrated in FIG. 3. The grinding machine and process is described in fall detail in the above mentioned patents. While this machine is generally acceptable, it produces a surface finish of 8 to 10 .mu. in R.sub.a (R.sub.a connotes roughness average) or greater. The grinding process is also very time consuming and expensive.
One machine capable of manufacturing items with very smooth surface finishes is a lapping machine. However, commercially available lapping machines are limited in that they are only capable of producing very smooth flat surfaces, i.e., lapped surfaces. Thus, a lapping machine cannot directly make a wavy face seal ring with a very low surface roughness.
It should therefore be appreciated that there is a need for a wavy face ring having a smooth lapped face and that there is a need for a method of manufacturing a wavy face ring with such a smooth lapped face. The present invention fulfills this need.